The present invention relates to a community antenna television (CATV) tap, and more particularly to one having remote subscriber service control
In CATV, a common antenna is used to pick up broadcast signals. These signals are amplified and feed into a transmission line. At intervals along the line are "taps" that pick off some of the transmission line signal and distribute it to, typically four, subscribers. If a subscriber should not pay his bill for the CATV service, it is desired by the CATV system operator to disconnect him. Because of the cost of sending a person to the tap, this should be done remotely from the signal source. This is accomplished by sending address digits on the line, which uniquely identify a tap and a subscriber coupled to that tap, and then sending control digits to turn off the service. A tap capable of so responding is called "addressable".
To actually cut off service, a variety of techniques have been used. One uses an electro-mechanical or electrical switch to attenuate the subscriber signal. A problem with such an approach is that a very high degree of attenuation, typically about 50 to 60 dB, is required to ensure that no detectable signal leaks through to the subscriber. This is expensive to achieve. Another technique is to jam the subscriber's signal. This requires an oscillator for every channel to be jammed, which is expensive, and the jamming signals can likewise be propogated into other subscriber's lines.
It is therefore an object of the present invention to provide an inexpensive subscriber service control function for an addressable tap.
It is a further object to provide one that causes a minimum of interference with other subscribers.
It is yet another object to provide an attenuator for such a tap that has a high degree of attenuation.